Wire coating apparatus and method



1961 H. B. LIT El'AL 2,994,624

WIRE COATING APPARATUS AND METHOD Filed Oct. 11, 1957 United StatesPatent 2,994,624 WIRE COATING APPARATUS AND METHOD B. Lit, Pittsfield,and Richard P. Anderson, 'Cheshire, Mass., assignors to General ElectricCompany, a corporation of New York Filed Oct. 11, 1957, Ser. No. 689,6035 Claims. (Cl. 117-232) The present invention relates to coatedelongated articles such as wire or the like, and more particularly to auniformly coated rectangular or other polygonal type of wire, to animproved process of applying a liquid coating composition on such wireto provide coatings of uniform thickness thereon, and to apparatusadapted for carrying out such process.

The invention is especially suitable for use in coating rectangularelectrical wire with viscous resin solutions, such as polyvinyl formal,to form an electrically insulating film thereon.

In the past, considerable difficulty has been encountered in obtaininguniformly thick coatings on wire of rectangular or other angularconfiguration. Due to the tendency of the applied liquid material toflow away from the corners of the wire and collect on the flat surfaces,inadequate deposit of coating was produced on the corners. As a result,the dielectric strength of the insulating film was substantially less atthe corners than at other parts of the wire. On the other hand,application of additional coats of liquid to overcome this difficultywas wasteful, since excessive coating material was thus deposited on theflat surfaces and made the coating build unnecessarily large.

It is an object of the invention to provide a uniformly coated wirehaving at least one flat side.

It is another object of the invention to provide a method of applying acoating of uniform thickness on wire or the like having at least oneflat side or having an angular cross section, and especially ofrectangular cross section.

It is still another object of the invention to provide a method ofpre-coating a rectangular wire or the like for the purpose ofcontrolling the subsequent deposition of layers of coating material onthe wire, whereby final insulating coatings of uniform thickness aroundthe con ductor are obtained.

It is a further object of the invent-ion to provide a wire coatingarrangement which is particularly effective and convenient for carryingout the above method.

Other objects and advantages will become apparent from the followingdescription and appended claims.

In one aspect of the invention there is provided a coated wire or thelike having at least one flat side, the wire having a uniformly thickcoating covering its sur face, the coating comprising a ridge of coatingmaterial on and extending along the flat side and a deposit of coatingmaterial on the remaining surface of the wire, the deposit of coatingmaterial having a thickness substantially equal to the height of theridge.

In another aspect, the present invention provides a method of producingan insulating coating of uniform thickness on a rectangular wire whichcomprises first forming on each of the flat sides of the wire at leastone ridge of the coating material extending along the Wire between itsopposite longitudinal edges, thereafter applying a hardenable liquidcoating material along the wire surfaces, and hardening the thus appliedliquid coating material.

In this connection, it will be understood that the term rectangular asused herein may also include a square shape.

In an embodiment of an apparatus which is adapted for effectivelycarrying out the above method, especially shaped die members arepreferably employed in the initial stages of the coating process forproducing the described foundation ridge of coating material, afterwhich the wire passes through die members of conventional constructionfor applying the subsequent film of hardenable liquid coating material.As a result of the provision of the coating ridge as described, thesubsequent deposition of liquid coating material uniformly about thewire is made possible.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a view in perspective of a portion of a continuous coatingapparatus which may be employed in carrying out the present invention;

FIG. 2 is a perspective view of a wire coating die device which may beincorporated in the apapratus shown in FIG. 1;

FIG. 3 is a cross-sectional view of a rectangular wire showing it inoperative relation with die members formed in accordance with anembodiment of the invention;

FIG. 3a is a cross-sectional view of the rectangular wire withfoundation ridges applied thereon by the means shown in FIG. 3;

FIG. 3b is a view similar to FIG. 3:: showing the finally coated wire;and

FIGS. 4-40 are views of various other embodiments of wire contacting diemembers which may be used in practicing the present invention.

Referring now to the drawing, and particularly to FIG. 1, there is showna continuous coating apparatus for coating a wire with a series ofapplications of insulating enamel and hardening by heat each coat afterit has been applied. For this purpose there is provided a lower guidesheave 1 having grooves to which wire 2 is led from a pay-off reel (notshown), the wire 2 passing from sheave 1 upwardly through vessel 3containing a supply of the resinous viscous enamel or varnish, such aspolyvinyl formal, to be applied to the wire. Wire 2 enters the bottom ofvessel 3 through a pad 5 of felt or the like which serves to retain thecoating liquid 4 in the vessel 3 at the wire inlet. After emerging fromthe vessel 3, wire 2 initially passes upwardly through die device 6a,constructed as more fully described hereinafter, which is carriedupwardly by the moving wire until restrained from further upwardmovement by spaced fingers 7, or other suitable stop means, which permitfree lateral or rotational movement of the die device in response to anyswaying or twisting movement of the wire. The stop pins 7 are secured toa bar 8 which in turn is mounted on a suitable support 9.

In passing upwardly through the various die devices 6a, 6b, 6c, 6d, andso on, wire 2 undergoes successive stages of application of coatingmaterial on the wire. In accordance with the invention, the die devicesin the first and also preferably in the second stage, as represented bydevices 6a and 6b, incorporate a pair of especially shaped die membersfor providing a foundation ridge of coating material on and extendingalong the opposite broad surfaces of the rectangular wire, as shown inFIGS. 3 and 3a. Thereafter in subsequent stages, the die devicesincorporate die coating members having conventional forms, such as shownin FIG. 2.

After each application of coating material, including those in the firsttwo stages, the wire 2 passes upwardly through a baking or drying oven10 of any suitable or conventional type wherein the varnish coatingapplied to the wire is heat-hardened. Thereafter, wire 2 passes aroundsheave 11 and back to drive sheave 1 to a groove spaced axially from theinitial receiving groove. The passage of wire through the apparatus inrepeated stages in the manner described, and shown in FIG. 1, results ina coating of the desired thickness being finally built up,

' 3 the total number of stages being normally about 6 to 8. The coatedwire is ultimately conducted to a take-up reel or other storage means(not shown).

FIG, 2 shows the structure of die device 6 in greater detail, and asillustrated therein the die comprises in a preferred embodiment a pairof flat plates 12 and 13 constituting the supporting frame of the dieand having slidably arranged in grooves therein pairs of movable diemembers 14, 15, 16 and 17, the die members being arranged to contact thesurfaces of the rectangular wire 2 as it passes through the die device.The die device having die members as shown in FIG. 2 may be used for thecoating stages Subsequent to the initial ridge-forming stages, but forthe ridge-forming stages the conventional die members 14 and 15contacting the broad sides of the wire are replaced by especially shapeddie members as more fully described and shown hereinafter.

The die device 6 shown in FIG. 2 is disclosed and claimed in ourcopending application Serial No. 594,044, filed June 26, 1956, andassigned to the same assignee as the present invention, now PatentNumber 2,875,725, is sued March 3, 1959. While this device may besuitably employed in connection with the present invention, it will beunderstood that other types of die coating devices may be used ifdesired.

It has been found that when die members are used which have edge facesuniformly spaced from or parallel to' the flat sides of the wire overtheir entire extent, the coating deposited tends to be non-uniform inthickness and, in particular, the coating on the corners of the wire isrelatively thinner than elsewhere on the wire surfaces. If such diemembers having relatively shallow grooves in serrated form are employed,this non-uniformity is manifested by a coating which tends to have anelliptical shape, resulting in excessive coverage of the centralportions of the flat sides of the wire and inadequate coverage of thecorners. On the other hand, when such die members have relatively deepserrations for applying somewhat thicker layers of enamel at each pass,the deposited coating assumes a distorted or so-called dog bone shapedue to the greater accumulation of deposit on the flat sides adjacentthe corners, and, in this case also, insufficient coating is provideddirectly on the corners.

. Although the reasons for these effects are not completely known, itappears that the form of the deposited liquid coating material on thewire is influenced by its surface tension, which draws the liquid towardthe flat surfaces and away from the corners. This effect and theconsequent non-uniformity of coating thickness appear to be even morepronounced in the case of relatively wide wire and when coating liquidof relatively low viscosity is used.

In accordance with the invention, the above difficulties are overcome byinitially providing a ridge or barrier of coating material along thefiat sides of the wire, and thereafter applying the coating proper inthe usual fashion using conventional die members. To this end there isprovided in the die coating devices in the initial stages of the wirecoating apparatus shown in FIG. l, die members 20 and 21 (FIG. 3) havinga particular construction for wiping the opposite side faces of Wire 2,in place of the usual members 14 and 15 shown in FIG. 2. Die members 20and 21 may be in a variety of forms, as shown in FIGS. 3 and 4-4cinclusive, but essentially they are pro vided with one or more recessesintermediate the outer edges of their contact edge faces for the purposeof depositing, prior to the application of the coating proper, one ormore barrier ridges along the faces of the wire.

As shown in FIG. 3, in the initial stages Wire 2 passes betweenstraight-edged die members 22, 23 contacting the narrow faces of thewire, and with its broad faces in contact with die members 20, 21 whichhave suitably shaped recesses 24, 25 therein. As the Wire passes throughthis die with liquid coating material thereon picked up from 4 V bath 4,the narrow sides and the margins of the broad sides of the wire arewiped substantially free of coatingmaterial by the flat edges of diemembers 20, 21, 22 and 23 while mounds or ridges 24, 25 of liquidmaterial are deposited on the opposite central wire portions by virtueof recesses 20a, 21a. The mounds 24, 25 after hardening in the bakingstage thus form solid barriers, which serve to separate on each sidethereof the liquid material deposited thereafter on the broad wire facesin subsequent passes of the wire.

Foundation mounds as described may be provided on any one or all of thesurfaces of the wire where deemed necessary or desirable. Thus, recesseddie members of the invention could also be used in place of die members22, 23, along with die members 20, 21, if wire 2 were square or its edgefaces likewise were rather wide.

FIG 3b shows the coated wire product 2 after the coating procedure iscompleted. As shown, the final coating surrounds the wire in uniformdepth and comprises ridges 24, 25 on the surface of the central portionsof the flat sides and the main coating deposit 30, having substantiallythe same thickness as the mounds 24, 25, on the remaining wire surfacecomplementing the ridges. The thickness of the coating 30 with respectto the wire is not necessarily as shown, and it may vary depending onthe degree of protection or insulation desired. It will be understoodthat the film 30 normally is comprised of a number of deposited layerscorresponding to the number of passes the wire undergoes in the coatingapparatus, but if desired only a single layer of appropriate thicknessmay be applied as, for example, by means of die members havingserrations of suitable depth.

FIGS. 4-40, inclusive, show various embodiments of the ridge-producingdies which may be used in the initial stages of the coating process toprovide a proper foundation on the wire in accordance with theinvention. In FIG. 4, the die member 26 has a rectangular groove 26a inits face, whereas die member 27 in FIG. 4a has a curved depression 27a.The ridge may also be pro duced by. a serrated form of recess 28a asshown in the member 28 of FIG. 4b. Normally, one recess in each diemember of the types shown or equivalent forms is adequate for wire ofordinary width. However, where relatively wide wire is to be coated, aplurality of such recesses 29a may be utilized, if desired, as shown indie member 29 of FIG. 40.

In general, it is preferable to deposit the foundation ridge centrallybetween the longitudinal edges of the wire, but satisfactory results mayalso be obtained even if the ridges are not located at the mid-points.

The ridge provided on the wire in accordance with the invention appearsto restrain or reduce the effect of surface tension of the coatingapplied in subsequent stages with the usual die members and to force thematerial to flow away from the central portions of the flat sides towardthe corners. As a result, it has been found that the elliptical and dogboning forms of deposited layers are largely avoided and insulatingcoatings of much more uniform thickness are obtained. 7

By provision of such foundation ridges, a fewer number of passes of thewire through the coating apparatus have been found to be necessary thanheretofore used to provide adequate corner coverage, and at the sametime excessive build of insulating enamel at the flat sides is avoided.

The following is a typical process for carrying out the presentinvention, it being understood that the procedure described is merelyillustrative and that the invention is not intended to be limited in anywayby the relative dimensions or other details set forth. sulatingvarnish composed of polyvinyl formal with a viscosity of 5000centipoises was used for coating rec-' tangular copper wire of 200 milswidth and mils.

thickness. For producing foundation ridges in" accord- A bath of in--mice with the invention on the 200 mil surfaces, die members were usedhaving an angular groove in their edge faces of 30 mils deep, a 60angle, and a base dimension of 35 mils. Passage of the wire through afirst set of recessed die members of the above construction provided amound on the 200 mil surfaces of 75 mils Width and about .5 mil high. Asecond pass through a similar set of die members produced a mound twiceas high. After providing such a mound, 6 or 7 additional passes are thenmade of the wire through the varnish bath and die members ofconventional construction to produce an insulating film of desiredthickness. In a usual procedure, the finished thickness at the end ofthe process would be about 2.5 mils. In general, a higher initial moundwould be provided for use where a greater thickness of ultimate coatingis to be applied in the coating procedure.

The die members used for the narrow edges of the wire, i.e., thoserepresented by members 22, 23 in FIG. 3, either in the initial orsubsequent passes of the wire, may have edge faces which are straight orof any other suitable form.

A series of tests were made to determine the coating and electricalcharacteristics of wire coated in accordance with the invention ascompared to that coated in the conventional manner. In these testsrectangular copper wire having a width of .236 inch and thickness of.132 inch was used for both processes, the liquid coating material beingpolyvinyl formal. The wire subjected to the conventional coating processwas moved through the continuous coating apparatus in six passes, eachpass being through standard types of serrated die members. The wiretreated in accordance with the present invention was likewise movedthrough the coating apparatus in six passes, but in this case the diemembers engaging the broad side faces of the wire in the first twopasses were ridge-producing devices having a 30 mil deep angular grooveof the type shown in FIG. 3, and in the remaining four passes thestandard serrated die members were used.

Measurements of the coating layers produced by these processes showedthat in the conventionally coated wire, the coating thickness on thebroad faces ranged from about 1.8 to 2.0 mils and on the narrow facesfrom about 2.2 to 2.4 mils, and the average dielectric strength of foursamples of this coated wire was found to be 2.3 kv.

In the case of the wire coated in accordance with the present invention,the finished coatings on the broad faces were uniformly 1.9 mils thickand on the edge faces 2.0 mils thick. The average dielectric strength offour samples of this wire was 4.8 kv.

It is evident from these tests that more uniform coating layers andmarkedly improved (over twice as great) dielectric strength characterizerectangular wire coated by the present process as compared to wireobtained by the conventional method, using the same number of coatingstages.

While the wire shown and described is of flat rectangular shape, it willbe understood that the invention is similarly applicable to wire orother elongated articles having other shapes including at least one flatsurface, such as square, triangular, half round, and other forms.

Because the foundation ridge provided by the present invention serves todirectly control the proper distribution of the subsequently appliedliquid coating material over the surfaces of the wire, it makesunnecessary the precise timing and temperature of the baking stage whichare relied on in certain prior methods, wherein excessive amounts ofliquid are first applied to the corners of the wire then allowed to flowtoward the central side portions for a predetermined period before beinghardened by baking.

It will be understood that the invention includes the application of thefoundation ridge to the wire broadly speaking, i.e., whether the wire isbare metal or already has a uniform film of insulating or other materialthereon,

since obviously the ridge need not be in direct contact with the wiremetal to achieve the purposes of the invention.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. The method of providing a coating of uniform thickness on wire andthe like having at least one fiat side, which comprises applying ahardenable liquid coating material on the wire, passing the wire withits flat side in engagement with a wiping surface having a recess formedtherein so that substantially all of the liquid coating material isremoved except that passing through said recess, hardening saiddeposited liquid coating material remaining on said flat side so as toform a solid ridge of coating thereon, applying hardenable liquidcoating material around the wire in sufiicient amount to provide on theremainder of the wire surface a coating having a thickness at leastequal to the height of said ridge, and hardening the thus applied liquidcoating material.

2. The method of providing a coating of uniform thickness on rectangularwire and the like having opposite fiat surfaces, which comprisesapplying viscous liquid coating material to said wire, passing the thuscoated wire through a die means for wiping off substantially all of saidliquid coating material except for a portion of said material extendingalong said opposite flat surfaces intermediate the longitudinal edges ofthe wire, heating the thus remaining portions of coating for formingsolid ridges thereof along the Wire, reapplying viscous liquid coatingmaterial around the wire, passing the wire through die means forproviding on the remainder of the wire 7 surface a thickness of the thusreapplied liquid coating material at least equal to the height of thefirst mentioned portion, and heating the coating material for hardeningthe same.

3. The method of providing a coating of uniform thickness on rectangularwire and the like having opposite flat surfaces, which comprisesapplying viscous liquid coating material to said wire; passing the thuscoated wire through a die means for wiping ofi substantially all of saidliquid coating material except for a portion of said material extendingalong said opposite fiat surfaces intermediate the longitudinal edges ofthe wire; heating the thus remaining portions of coating for formingsolid ridges thereof along the wire; forming a deposit of said coatingmaterial around the wire by reapplying the viscous liquid coatingmaterial around the wire, passing the wire through die means forreducing the thickness of the thus reapplied liquid coating ma terialand heating the coating material for hardening the same; and repeatingsaid last mentioned deposit forming procedure until a coating of athickness at least equal to the height of the ridges is obtained on theremainder of the wire surface.

4. Apparatus for providing wire and the like having at least one flatside with a coating of uniform thickness comprising, in combination,means for applying viscous liquid coating material to the surfaces ofthe wire, means for providing a ridge of coating material along the flatside intermediate its longitudinal edges while wiping the remainder ofsaid flat side substantially free of the applied liquid coatingmaterial, and means for applying a coating of liquid material ofpredetermined thickness around said wire along the length thereof.

5. Apparatus for providing rectangular wire and the like with a coatingof uniform thickness comprising, in combination, means for applyingviscous liquid coating material on the surfaces of said wire, means forproviding a ridge of coating material along the :flat sides of said wireintermediate its longitudinal edges while wiping the remainder of saidflat sides substantially free of the applied liquid coating material,said ridge producing means comprising a pair of die members contactingthe opposite fiat sides of said wire, each die member having a wirewiping surface, said surface being formed only in a substantiallycentral portion thereof with at least one recess and being substantiallyflat in the remainder of its wire wiping surface, and means for applyinga coatsaid wire along the length thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,287,589 Wilson et al. June 23, 1942 2,345,390 Flynn Mar. 28, 19442,346,697 Mungall Apr. 18, 1944 2,433,642 Bailey Dec. 30, 1947 2,447,521Miller et a1 Aug. 24, 1948 2,782,563 Russell Feb. 26, 1957 2,812,741OConner Nov. 12, 1957 2,875,725 Lit et a1. Mar. 3. 1959

1. THE METHOD OF PROVIDING A COATING OF UNIFORM THICKNESS ON WIRE ANDTHE LIKE HAVING AT LEAST ONE FLAT SIDE, WHICH COMPRISES APPLYING AHARDENABLE LIQUID COATING MATERIAL ON THE WIRE, PASSING THE WIRE WITHITS FLAT SIDE IN ENGAGEMENT WITH WIPING SURFACE HAVING A RECESS FORMEDTHEREIN SO THAT SUBSTANTIALLY ALL OF THE LIQUID COATING MATERIAL ISREMOVED EXCEPT THAT PASSING THROUGH SAID RECESS, HARDENING SAIDDEPOSITED LIQUID COATING MATERIAL REMAINING ON SAID FLAT SIDE SO AS TOFORM A SOLID